Bolsters and side frames are key parts for the running gear of railway trucks. The layered and sectioned manufacturing are generally by the core-making technique for forming the sand core of the core cavity in the process of manufacturing the bolster and side frame casts in China, and even throughout the world, as shown in FIGS. 1 and 2.
For adopting the layered and sectioned core-making techniques, the produced bolster and side frame mainly have disadvantages in two aspects:
The first disadvantage: the sand core connection part has an uneasily controlled gap due to sand core deformation or edge breakage, as shown in FIG. 5. The gap 3 makes the core cavity form a flash, especially a flash in the cavities corresponding to the key parts A and B of the bolster and side frame during the casting and shaping processes. And the connection part of the flash and the core cavity easily produces subsurface pores 8 and micro-cracks 7 during the solidification process of casts with flashes in the core cavity, as shown in FIG. 6. The subsurface pores 8 and micro-cracks 7 are not easily detected by common product testing because they are located in the core cavity, for example, which brings potentially dangerous qualities to products. As the key parts of the running gear of railway trucks, the bolster and the side frame have the pores and micro-cracks inside the cast which act as stress sources under the continuous cyclic stress during the operation of the railway truck. The stress gradually escalates, thus largely shortening the service life of the product. More seriously, micro-cracks gradually escalate and result in breakage of bolsters and side frames which causes a railway accident.
The second disadvantage: a core chaplet 9 is always used in order to strengthen the sand core location and ensure the cast wall thickness conforms to the requirements after core setting and before mould assembling when layering and sectioning the sand core, and the amount of the bolster or side frame used is more than 30, as shown in FIG. 7. The use of a core chaplet influences performance of the cast in the following three aspects: firstly, the core chaplet is not easy to fuse with the cast, thus reducing the useful sectional area of the cast, and producing partial stress to the corresponding part. The disadvantage of such stress, more specifically, is that the starting point of the micro-cracks gradually escalates under the cyclic stress and the stress can only be discovered by fatigue testing more than millions and even tens of millions of times. Secondly, the surface of the core chaplet easily erodes, and pores are generated during casting, and the plated tin or zinc reacts with molten steel though contacting, thereby making a byproduct in the partial cast which can be segregated to form a stress source so as to affect performance. Thirdly, when in use, the dropped upper mould sand 10 which is squeezed by the core chaplet directly falls into the mould cavity, as shown in FIG. 7, forming sand holes inside or on the surface of the cast. And the sand holes formed on the cavity surface are not easy to get rid of, leaving potential dangers in operation.
The main disadvantages above mentioned usually arise in railway operation, causing interruption of railways, and bringing great social and economic losses to railway transportation.
One-piece core making is required in order to eliminate such disadvantages. A common one-piece core-making solution uses a core shooter to shoot a core. The core shooting technique is usually a half-and-half type with a horizontal (transverse) mould closing. But the core shooter equipment is complicated, expensive and has high requirements for power, controlling parts and installation. Moreover, the sand core is partially over compacted and non-uniformly compacted, resulting in the generation of cracks in the cast.